Observer-based control of a walking planar biped robot: Stability analysis

In this paper, the problem of the estimation of the absolute orientation of a dynamical stable five-link biped during a walking gait is tackled. The proposed solution is founded on the design of a nonlinear observer based on the "super-twisting" approach, such that the estimation error converges in finite time and only uses the measurements of the joint variables. This observer is coupled to a nonlinear control law which also converges in finite-time. The stability of the cyclic walking gait under the observer-based controller is proved.